Design, construction, and calibration of an Avalanche-confinement Tissue Equivalent Proportional Counter (AcTEPC) for Radiation Monitoring in Space and Therapeutic Applications

The same absorbed dose from different fields of ionizing radiation (IR) can produce different effects on biological targets. This is due to the random or stochastic nature of radiation interaction with matter, (i.e. the local energy depositions and ionization clusters produced in DNA strands and chromatin fibers). These events are currently considered to be the starting point of radiation-induced damage. To precisely account for this, a radiation detector capable of measuring this radiation quality in tissue sites of nanometric dimensions has been proposed. It is the so-called Avalanche-confinement Tissue Equivalent Proportional Counter (AcTEPC). This AcTEPC employs a rather unconventional geometry of the gasfilled sensitive volume (SV) different from the conventional spherical or cylindrical types. It is made up of a hexagonal cathode shell housing two other electrodes – i.e. a hexagonal grid of parallel wires surrounding a central anode wire. These three electrodes are biased independently. The grid sub-divides the SV into an external drift region (DR) where primary ionizations occur and an internal multiplication region (MR) that amplifies these primary currents to produce a readable signal at the anode. Preliminary studies evaluated the performance of this proposed prototype using analytical models, COMSOL Multiphysics and Monte Carlo (MC) simulations for different particle beams and simulated site. Results suggested an isotropic response and the capability to simulate tissue response for any IR field. These preliminary results serve as proof of concept and highlight significant improvements that can still be made in radiation detector design.